Method of producing composite concrete - steel pipes and joints and pipe and joint obtained by means of said method

ABSTRACT

1. Method of producing a composite concrete-steel pipe comprising the steps of taking a thin mild steel sleeve to SERVE AS THE INNER WALL OF THE PIPE, ATTACHING METAL REINFORCING MEANS TO THE OUTER FACE OF SAID SLEEVE, FORMING AN INJECTING MOULD ABOUT SAID SLEEVE BY PLACING MEANS ACTING AS A MOISTUREPERMEABLE ENCLOSURE AROUND SAID SLEEVE, SAID ENCLOSURE CONSTITUTING THE OUTER WALL OF SAID MOULD AND SAID SLEEVE CONSTITUTING THE INNER WALL OF SAID MOULD, INJECTING COLLOIDAL CONCRETE INTO SAID MOULD, COMPRESSING THE CONCRETE BEFORE IT HAS SET BY CREATING AN INTERNAL HYDRAULIC PRESSURE IN SAID SLEEVE SO AS TO EXPAND SAID SLEEVE BEYOND THE ELASTIC LIMIT OF SAID MILD STEEL, RELEASING SAID HYDRAULIC PRESSURE IN SAID SLEEVE AFTER HARDENING OF THE CONCRETE, AND REMOVING THE RESULTING COMPOSITE CONCRETE-STEEL PIPE COMPRISING SAID CONCRETE, SAID REINFORCING MEANS AND SAID MILD STEEL SLEEVE EXPANDED AGAINST SAID CONCRETE.

United States Patent 1191 Lamy Sept. 18, 1973 [54] METHOD OF PRODUCING COMPOSITE 1,310,597 7/1919 Blaw 138/153 CONCRETE STEEL PIPES AND JOINTS 3,077,008 2/1963 Deflon 138/153 AND PIPE AND IDINT DDIAINDD DY 13331222 1111352 111211111... 1111111111111111111251313 MEANS OF SAID METHOD 2:754:563 7/1956 Hartenstein. 25/126 [75] Inventor: Jacques Edouard Jean Lamy, 3,183,572 5/1965 Fritz 25/126 Fontenay-Aux-Roses, France Primary ExaminerCarl D. Quarforth [73] Assigneez Socrete DEtude du Transport et de Assistant Examiner Roger S. Gaither La Valorisation Des Gaz Naturels du Att0mey R0ben Bums Sahara S.E.G.A.N.S.", Paris 6cm) France EXEMPLARY CLAIM [22] Ffled: 1964 1. Method of producing a composite concrete-steel [21] Appl. No.2 415,561 pipe comprising the steps of taking a thin mild steel sleeve to serve as the inner wall of the i e, attaching metal [30] Foreign Apphcanon Pnomy Dan reinforcing means to the out r face of said sleeve, Nov. 25, 1963 France 63954915 forming an injecting mould about said sleeve by placing means acting as a moisture-permeable [52] US. Cl 29/460, 425/63, 264/228, enclosure around said sleeve, said enclosure 29/4711 constituting the outer wall of said mould and said [51] Int. Cl B23k 31/02, B28b 17/00 Sleeve constituting the inner wall of said mould [58] Fleld of Search 264/228; 25/118 T; injecting colloidal concrete into Said mould 425/63; 29/460 4711 compressing the concrete before it has set by creating an internal hydraulic pressure in said [56] References Clad sleeve so as to expand said sleeve beyond the UNITED STATES PATENTS elastic limit of said mild steel, releasing said 2,311,358 2 1943 Baily 25/118 T hydraulic PIDSSIIID in said Sleeve after hardening of 2,474,660 6/1949 Fitzpatrick 264/228 the concrete, and removing the resulting 2,582,751 1/1952 Fitzpatrick 264/228 composite concrete-steel pipe comprising said 2,709,845 6/1955 Se n 1 264/228 concrete, said reinforcing means and said mild 3,260,020 7/1966 Patin 264/228 Steel Sleeve expanded against said concrete 3,172,932 3/1965 Vander Heyden. 264/228 3,182,109 5/1965 Grevlich 264/228 6 Claims, 8 Drawing Figures SHEU 3 [1F 4 PATENTED SEP] 8 I973 SHEET '4 OF 4 m W m? 2 METHOD OF PRODUCING COMPOSITE CONCRETE STEEL PIPES AND JOINTS AND PIPE AND JOINT OBTAINED BY MEANS OF SAID METHOD Several methods of producing concrete pipes are already known which employ hooping or reinforcements which are placed in position before pouring the concrete and are thus embedded in the latter and are thereafter put under tension by the expansion of the concrete caused by a high pressure applied to the inner wall of the pipe until the concrete has set and hardened.

After the concrete has set and hardened, the internal pressure is removed and the pipe is then subjected to radial, transverse and longitudinal compressive stresses owing to the tension of the reinforcements.

Such pipes are suitable, for example, for irrigation pipe-lines or forced-supply conduits but can not be used in their normal state for transporting liquid or gaseous hydrocarbons.

The object of the invention is to provide a method of producing composite concrete-steel pipes, for example pipes of vary large diameter capable of withstanding high pressures, which it is not possible to obtain at the present time with weldable steel grades available in the industry.

Another object of the invention is to provide a method of producing such pipes which are suitable for conducting hydrocarbons.

The invention provides a method of producing concrete-steel pipes and joints in which the concrete is subjected to a triple stress owing to a single internal pressure and which comprises injecting a colloidal concrete between a thin mild steel sleeve forming the inner wall of the pipe or joint, and an outer enclosure, said outer enclosure being either constituted by a concrete-drying removable shell structure provided with a clamping device, a winding of steel wire being in this case embedded in the concrete, or being part of the pipe, in which case the enclosure is constituted by a winding of contiguous coils, said winding performing the functions of a transverse prestressing hooping, a concrete drying means and a permanent outer enclosure.

Another object of the invention is to provide an apparatus for carrying out said method, said apparatus comprising in combination, handling devices for placing the skeleton of the pipe in position and for shifting the concrete steel pipe, closing means for closing the ends of the annular chamber receiving the injection of concrete and closing the inner sleeve of the pipe, a vessel for injecting the concrete under pressure, connecting means connecting the vessel to the annular chamber, a source of water under pressure, connecting means connecting the source to the inner space of the sleeve and a press for maintaining the pipe closed during the application of said internal pressure.

A further object of the invention is to provide a pipe and a joint permitting straight or other pipe connections, said pipe or joint being of the composite concrete-steel type and comprising a mild steel inner collar and an outer mass of concrete and an outer winding having contiguous coils in which the concrete is subjected to a triple stress created by a single internal pressure.

Further features and advantages of the invention will be apparent from the ensuing description, with reference to the accompanying drawings to which the invention is in no way limited.

In the drawings:

FIG. 1 is a partial cross-sectional view of a first embodiment of a composite concrete-steel pipe according to the invention, this pipe having embedded coils;

FIG. 2 is a longitudinal half-sectional view of said pipe, taken along the broken line 2-2 of FIG. 1;

FIG. 3 is a partial perspective view of a detail of the ribbing of the sleeves FIG. 4 is a longitudinal elevational view partly in section, of the station at which the concrete is injected and the mixed pipe extracted;

FIG. 5 is a cross-sectional view of said injection and extraction station;

FIG. 6 is a partial cross-sectional view of a second embodiment of a compostie concrete-steel pipe having contiguous coils according to the invention;

FIG. 7 is a longitudinal sectional view, taken along the broken line 77 of FIG. 6, and

FIG. 8 is a partial longitudinal sectional view of a composite joint having contiguous coils for such composite pipes.

In the embodiment shown in FIGS. 1 and 2, the composite concrete-steel pipe according to the invention comprises an inner sleeve 1, which can have, for example, a thickness of 5 mm and is constructed from extra mild steel sheets bent and welded together. These sheets constitute the inner wall of the composite concrete-steel pipes.

In the embodiment shown in FIGS. 1 and 2, there are secured to this sleeve by welding rib structures 2 consisting, for example, of two metal bars 2a, 2b which have a corrugated configuration and are welded to a longitudinal metal bar 2c. The bars 2a and 2b can have, for example, a diameter of 5 mm and the bar 20 a diameter of 12 mm. These bars are advantageously of the type employed in concrete structures and hardened by torsion, such as the bars known under the name Tor bars or other highly adherent bars of hardened steel.

These longitudinal rib structures can also be composed of thin bent sheet, for example having a thickness of 1.5 mm. However, the aforementioned structure is preferred since it permits a better distribution of the concrete 3 which surrounds the bars, and as this rib structure is more deformable, the inner mild steel sleeve is not deformed thereby.

The sleeve receives at each end (FIG. 2) two apertured rims 3a, 3b between which extend the wires or rods 4 for producing the longitudinal pre-stressing. These wires are flattened at their ends and held in the rims by screwed sleeves 5 whereby it is possible to put the wires under tension.

Hooping of the pipe is insured by two windings 6 and 7 which are separated by a steel wire or rod 8 which can be disposed helically so as to maintain the spacing between said windings. These windings can be composed of a single strand, two strands as shown in FIGS. 1 and 2, or several strands.

This hooping and the longitudinal Wires or cables are composed of hard steel wire of conventional type employed in pre-stressed concrete structures.

To produce the pipe, the equipped sleeve assembly just described is first constructed.

The production of the. pipe comprises the following 'stages.

1. Construction of the sleeve proper, composed of welded sheet metal, by conventional methods, so that there is no need to describe it in detail.

2. The fixing of the rims.

3. Mounting of the rib structures and the welding thereof to the sleeve so as to obtain the ribbed sleeve shown in FIG. 3, the rib structures being placed in position on the sleeve by a feeder and welded by a welding device mounted on a trolley.

4. Placing in position the longitudinal wires 4 and the sleeves 5 for putting these wires under tension. 5. Winding of the hooping by means of a special winding machine in which the ribbed sleeve is placed in position between two face-plates by means of a set of hydraulic jacks, a driving face-plate rotating the ribbed sleeve while a device similar to a saddle moves longitudinally as it winds one or a plurality of wires round the sleeve at a pitch which is adjustable.

This sleeve thus equipped constitutes a skeleton which is conducted by mechanical handling means to an injection station.

Such a winding machine is similar to a conventional winding machine, at least as concerns its principle of operation, and there is consequently no need to give a more detailed description thereof.

The injection and extraction station 11 is shown in FIG. 4, in which reference numeral 12 designates one end of a hydraulic press annexed to this station, the assembly constituting the essential part of an apparatus for producing finished pipes from the ribbed and equipped sleeves 13 (FIG. 5) described hereinbefore.

The injection and extraction station comprises (FIG. 4) an assembly of two gantries 14a, 14b provided with winches 15a, 15b and movable along runways 16 (FIG. 5) between an injection vessel 17 and a horizontal hydraulic press 12. The sleeve can be supported within these gantries at two points intermediate its ends by jacks 18, on mould-stripping jacks and at its ends by two jacks 19 on centering jacks, provided with rollers.

The two ends of the pipe can be closed by closing means 20 which are supported by carriages 21 which are movable along slideways 22 by hydraulic jacks 23 so that these closing means can be fitted onto the metal skeleton, namely the equipped sleeve 13. These closing means are connected by flexible pipes 24 to the injection vessel 17.

Disposed above the skeleton 13 is a drying or draining shell structure 25 (FIGS. 4 and 5) carried by a horizontal support bar 15c supported by the winches 15a, 15d of the gantries. This shell structure is composed of two part-cylindrical segments, namely a median segment 25a, and two lateral segments 25b, 25c. The shell structure 25 is suspended from the bar 150 by toggle devices 26 comprising links which are articulated in such manner that these toggle devices open when they are raised by the winches (position I shown in FIG. 5) and close when the central part of the toggle device descends and encounters the skeleton 13 (position II in FIG. 5). When the cable of the winches becomes slack, the closure of the shell structures can be almost complete and can be completed by the action of two horizontal jacks 27.

The three parts of the drying or draining shell structure consist of staves of wood. When they are in the closed position on the sleeve they form the cylindrical outer wall of the mould whose cylindrical inner wall is formed by the sleeve, the plane end faces of the mould being formed by the closing means 20 which are consequently the mould ends; the closing means 20 are equipped with sealing elements so as to close the mould in a sealed manner. These mould ends have concrete injection apertures which communicate with the annular chamber of the mould and a plurality of water inlets which are provided with stop valves and communicate with the chamber of the sleeve. Further, these various apertures are provided with closing valves of conventional type.

The concrete injection aperture or apertures are connected to the injection vessel 17 by the pipe or pipes 24, the water inlet aperture is connected to a source of water under pressure (not shown).

The mould ends have recesses which are so disposed and dimensioned as to be capable of accomodating the sleeves 5 (FIG. 2) when these mould ends are placed in position on the ends of the mould.

The draining or drying shell structure 25 can be hooped by means of binding cables 28 for example disposed in pairs in transverse planes. These cables are provided at their ends with tightening means such as threaded sleeves which can be tightened together by means of a screw having opposite threads and a ratchet lever or the like.

The press 12, constituting a part of the apparatus, comprises a fixed bench 29 and two horizontal clamping jacks 30 which are symmetrically opposed to one another.

The apparatus is completed by accessories such as shelters 31a, 31b and floors such as 32.

The apparatus is used and operates in the following manner.

A ready-made skeleton or ribbed reinforcement such as 13a (FIG. 5), is raised, brought to the position 13, and centered by the jacks 19 so as to make the axis of the skeleton coincide with the axis of the'mould ends and bring the sleeves 5 in alignment with their recesses by the sliding of the carriages 21 controlled by the jacks 23. The mould ends are then fitted onto the skeleton.

The shell structure 25 fed by the gantries is lowered onto the skeleton, from the position I to the position [I shown in FIG. 5 after which the jacks 27 completely close the shell structure round the sleeve.

Colloidal concrete is then injected under compressed air pressure by way of the pipes 24. When the mould is full, the air pressure, which is maintained for a few minutes, initiates the drying or draining of the liquid part of the concrete.

After the concrete pipes 24 have been disconnected, the assembly comprising the shell structure 25, the skeleton l3, and the mould ends 20 is conveyed by the gantries to the horizontal press 12 and placed between the two opposed clamping jacks 30. The water inlet is then connected to a source of water under pressure, and the volume within the mild steel sleeve is filled with water, the pressure of which is raised progressively.

Uner the effect of the internal pressure, the concrete is dried or drained through the staves of the shell structure and thus puts the hooping under tension, this hooping (FIG. 1 and 2) comprising the embedded coils 6 and 7 and the longitudinal wires 4.

In order to accelerate the hardening of the concrete, a stoving by means of steam is effected for some hours.

The shell structure 25 is returned to the injection station by the gantries, which roll along their rails 16, and

lowered by the winches until the mould ends rest on their sliding cradles or carriages 21.

The jacks 27 open the shell structure which is lifted away by the gantries and thus releases the stoved pipe under which are placed two platforms 18a raised by the jacks 18.

The stoved pipe is then emptied of the water it contains under pressure and this results in a partial release of the stress in the steel wires having a high elastic limit and in the sleeve whose elastic limit was exceeded under the effect of the pressure. In this way, a triple stressing of the concrete is achieved.

The mould ends 20 are extracted from the pipe by the carriages 21 which are moved along their slideways 22 by the hydraulic jacks 23.

The finished pipe 33 having embedded coils is then rolled away. A new skeleton is placed in front of the injection station and held by the centering jacks 19 while the platforms of the jacks l8 descend.

The pipe according to the invention can be constructed in accordance with another embodiment,

shown in FIGS. 6 and 7, which differs from the first embodiment in that the hooping, instead of being obtained by means of non-contiguous coils 6 and 7 embedded in the concrete, is obtained by means of coils 41 which are mounted about longitudinal wires 20 as in the first embodiment but are in contiguous relation to each other so as to form a cylindrical outer wall covered by a protecting covering 42 which can be, for example, composed of an epoxy pitch or of a polyester resin reinforced with chopped glass fiber.

The method of producing this pipe and the apparatus therefor are consequently modified owing to the fact that the wall provided by the contiguous coils constitutes the outer wall of the mould and that the use of a drying shell structure and tightening hooping is no longer necessary.

The rib structure (2a, 2b, 2c) is secured to the sleeve in the manner described with respect to the first em bodiment, then the contiguous coils 41 are wound under slight tension by a winding machine with a steel wire of the type employed in the conventional manner in pre-stressed concrete structures. The longitudinal pre-stressing wires 4 and the sleeves 5 (FIGS. 6 and 7) are mounted as in the first embodiment.

The other operations for producing this pipe having contiguous coils are similar to those described in respect of the first embodiment. However, as no concrete drying shell structure having the same length as the length of pipe is employed, the spacing between the gantries must be greater than that in the first embodiment since in order to handle the pipes the mould ends must be hooked to the gantries. After injection, the pipe is subjected to the internal pressure of the water as in the first embodiment. Under the action of this pressure the concrete is dried through the winding of contiguous coils, the latter being put under tension in the same way as the longitudinal wires. When the water is drained away, after stoving, the tension of the steel wires is partially released and there is obtained a triple stressing the greatest of which is in the transverse direction and can reach as much as 600 k'g/sq cm.

This winding having contiguous coils thereafter receives the protecting covering 42, the latter being applied when this pipe has just been extracted from the injection station and is still hot.

For this purpose, this pipe is placed by a centering system, for example, by means of jacks, between two face-plates, one of which is a driving face-plate and drives the pipe in rotation. A carriage, which moves along a generatrix simultaneously effects a scouring operation by sanding and the application of the covering.

The residual heat of said pipe having contiguous coils coming from the stoving is such that it accelerates the polymerisation of the covering and thus increases its effectiveness. The finished pipe is then dried.

The scope of the invention also embraces a joint I (FIG. 8) whereby it is possible to interconnect two pipes T1, T2 of the type described hereinbefore.

This joint employs the bare end portions Ea, Eb of the sleeves 1a, lb of two pipes 2a, 2b which, in the case shown in FIG. 8, are pipes of the type having contiguous coils. Such end portions, which were utilized for fitting the mould ends, have not varied in diameter during the pressurizing of the pipe and still have the required dimensions. These end portions are fitted together with the aid of a suitable expansible inner collar and then welded at 51.

The annular joint J which surrounds the end portions Ea, Eb comprises an annular support 52 provided with an injection aperture 53, and a hooping 54 having contiguous coils. For its manufacture, the joint further comprises a flexible annular chamber 55 provided with an injection pipe 56 and surrounding a protecting ring 57. This chamber can be a toric chamber or a rectilin ear chamber wound round the ring 57. The joint further comprises a mass of poured concrete 58 and is preferably constructed on the site.

The annular members (ring 57, toric chamber 55, annular support 53 and hooping 54) are slipped on one of the pipes prior to the coupling of the pipes and prior to the welding of the two sleeves la, lb. The concrete 58 is thereafter injected, then the chamber 55 is filled with a hardening substance, such as the product known under the trade name of Brauthite, which is introduced under pressure by way of the pipe 56. This expands the chamber 55, the concrete undergoes an inner radial compression and is dried and furthermore puts the hooping 54 under tension.

The internal pressure is maintained until the substance filling the chamber 55 hardens.

This joint is thus rendered as strong as the pipes it connects.

As it can be constructed in the form of a biased joint, the joint permits in most cases following the desired path for the pipe-line, irrespective of the sinuous nature of the pipe-line.

Thus, it is merely necessary to construct straight I composite pipes according to the method of the invention, although it is possible to produce bent pipes which are also embraced by the scope of the invention.

Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

For example, the longitudinal stress can be obtained without the longitudinal wires 4 by the following method which constitutes a variant of the invention.

According to this variant, the mould ends are fitted onto the sleeve and maintained in position by means of an automatic clamping by jacks disposed in a ring. The internal hydraulic pressure then permits not only radially expanding the sleeve but also extending it longitudinally, this extension creating after the hardening of the concrete and the elimination of the hydraulic internal pressure, a longitudinal compression of this concrete and consequently a third stress. In this case, the forces exerted on the mould ends must be wholly supported by the press 12 shown in FIG. 4 whereas in the previously-described methods of production the longitudinal steel wires 4 are capable of withstanding all or a part of the forces exerted on the mould ends depending on the number and cross section of these wires.

Having now described my invention what I claim as new and desire to secure by letters patent is 1. Method of producing a composite concrete-steel pipe comprising the steps of taking a thin mild steel sleeve to serve as the inner wall of the pipe, attaching metal reinforcing means to the outer face of said sleeve, forming an injecting mould about said sleeve by placing means acting as a moisture-permeable enclosure around said sleeve, said enclosure constituting the outer wall of said mould and said sleeve constituting the inner wall of said mould, injecting colloidal concrete into said mould, compressing the concrete before it has set by creating an internal hydraulic pressure in said sleeve so as to expand said sleeve beyond the elastic limit of said mild steel, releasing said hydraulic pressure in said sleeve after hardening of the concrete, and removing the resulting composite concrete-steel pipe comprising said concrete, said reinforcing means and said mild steel sleeve expanded against said concrete.

2. Method of producing a composite concrete-steel pipe compirsing the steps of taking a thin mild steel sleeve constituting the inner wall of the pipe, attaching reinforcing means to'the outer face of said sleeve, said reinforcing means comprising a winding of steel wire encompassing said sleeve, placing a removable concrete-drying shell structure around said sleeve and reinforcing means and combining said structure and said sleeve to constitute an injection mould, injecting colloidal concrete into said mould, compressing said concrete before it has set by hydraulically creating an internal pressure in said sleeve so as to expand said sleeve, releasing said pressure in said sleeve after hardening of said concrete, and removing from said shell structure the composite pipe thus constructed comprising said concrete, said reinforcing means and said sleeve attached to said reinforcing means.

3. Method of producing a composite concrete-steel pipe comprising the steps of: taking a thin mild steel sleeve constituting the inner wall of the pipe, attaching reinforcing means to the outer face of said sleeve, forming the outer wall of the pipe by surrounding said sleeve and reinforcing means by a winding of steel wire having contiguous coils, said outer wall being permeable to moisture and defining an annular space about said sleeve, closing said annular space to form an injection mould, injecting colloidal concrete into said mould, compressing said concrete before it has set by hydraulically creating an internal pressure in said sleeve, releasing said pressure in said sleeve after hardening of said concrete, and removing the resulting composite pipe comprising said outer wall of steel wire, said concrete, said reinforcing means and said sleeve attached to said reinforcing means.

4. Method of producing a composite concrete steel pipe comprising the steps of taking a thin mild steel sleeve constituting the inner wall of the pipe, fixing reinforcing means to the outer face of said sleeve, placing means acting as a moisture permeable enclosure around said sleeve, said enclosure performing the function of the outer wall of an injection mould and said sleeve performing the function of the inner wall of said mould, injecting colloidal concrete into said mould compressing the concrete before it has set by creating an internal hydraulic pressure in said sleeve so as to expand said sleeve, releasing said hydraulic pressure in said sleeve after hardening of the concrete, and removing the resulting composite concrete-steel pipe comprising said concrete, said reinforcing means and said steel sleeve fixed to said reinforcing means.

5. Method as claimed in claim 4 comprising creating said internal hydraulic pressure while allowing said sleeve to exapnd axially as well as diametrally, whereby the concrete is put under longitudinal compression after the setting of the concrete and elimination of said internal pressure.

6. Method of producing a pipe assembly comprising two composite concrete-steel pipes and a composite concrete-steel joint between said pipes, said method comprising producing each of said pipes by the following steps: taking a thin mild steel sleeve constituting the inner wall of the pipe, fixing metal reinforcing means to the outer face of said sleeve, placing a moisture permeable enclosure around said sleeve, said enclosure performing the function of the outer wall of an injection mould and said sleeve performing the function of the inner wall of said mould, with the end portions of said sleeve extending out of said enclosure, injecting colloidal concrete into said mould, compressing the concrete before it has set by creating with fluid means an internal pressure in said sleeve so as to expand said sleeve, releasing said pressure in said sleeve after the hardening of the concrete; placing a flexible annular container on one of said end portions of the sleeve of one of said pipes; fixing said one of said end portions to an end portion of the sleeve of the other of said pipes; placing a second moisture-permeable enclosure around said pipes in the region of said interconnected end portions of the sleeves; injecting concrete into the space defined by said second enclosure and said pipes; injecting under pressure a hardenable material into said flexible container so as to expand said container and compress said concrete in said space, and maintaining said material under pressure until it has hardened. 

1. Method of producing a composite concrete-steel pipe comprising the steps of taking a thin mild steel sleeve to serve as the inner wall of the pipe, attaching metal reinforcing means to the outer face of said sleeve, forming an injecting mould about said sleeve by placing means acting as a moisturepermeable enclosure around said sleeve, said enclosure constituting the outer wall of said mould and said sleeve constituting the inner wall of said mould, injecting colloidal concrete into said mould, compressing the concrete before it has set by creating an internal hydraulic pressure in said sleeve so as to expand said sleeve beyond the elastic limit of said mild steel, releasing said hydraulic pressure in said sleeve after hardening of the concrete, and removing the resulting composite concrete-steel pipe comprising said concrete, said reinforcing means and said mild steel sleeve expanded against said concrete.
 2. Method of producing a composite concrete-steel pipe compirsing the steps of : taking a thin mild steel sleeve constituting the inner wall of the pipe, attaching reinforcing Means to the outer face of said sleeve, said reinforcing means comprising a winding of steel wire encompassing said sleeve, placing a removable concrete-drying shell structure around said sleeve and reinforcing means and combining said structure and said sleeve to constitute an injection mould, injecting colloidal concrete into said mould, compressing said concrete before it has set by hydraulically creating an internal pressure in said sleeve so as to expand said sleeve, releasing said pressure in said sleeve after hardening of said concrete, and removing from said shell structure the composite pipe thus constructed comprising said concrete, said reinforcing means and said sleeve attached to said reinforcing means.
 3. Method of producing a composite concrete-steel pipe comprising the steps of: taking a thin mild steel sleeve constituting the inner wall of the pipe, attaching reinforcing means to the outer face of said sleeve, forming the outer wall of the pipe by surrounding said sleeve and reinforcing means by a winding of steel wire having contiguous coils, said outer wall being permeable to moisture and defining an annular space about said sleeve, closing said annular space to form an injection mould, injecting colloidal concrete into said mould, compressing said concrete before it has set by hydraulically creating an internal pressure in said sleeve, releasing said pressure in said sleeve after hardening of said concrete, and removing the resulting composite pipe comprising said outer wall of steel wire, said concrete, said reinforcing means and said sleeve attached to said reinforcing means.
 4. Method of producing a composite concrete steel pipe comprising the steps of taking a thin mild steel sleeve constituting the inner wall of the pipe, fixing reinforcing means to the outer face of said sleeve, placing means acting as a moisture permeable enclosure around said sleeve, said enclosure performing the function of the outer wall of an injection mould and said sleeve performing the function of the inner wall of said mould, injecting colloidal concrete into said mould compressing the concrete before it has set by creating an internal hydraulic pressure in said sleeve so as to expand said sleeve, releasing said hydraulic pressure in said sleeve after hardening of the concrete, and removing the resulting composite concrete-steel pipe comprising said concrete, said reinforcing means and said steel sleeve fixed to said reinforcing means.
 5. Method as claimed in claim 4 comprising creating said internal hydraulic pressure while allowing said sleeve to exapnd axially as well as diametrally, whereby the concrete is put under longitudinal compression after the setting of the concrete and elimination of said internal pressure.
 6. Method of producing a pipe assembly comprising two composite concrete-steel pipes and a composite concrete-steel joint between said pipes, said method comprising producing each of said pipes by the following steps: taking a thin mild steel sleeve constituting the inner wall of the pipe, fixing metal reinforcing means to the outer face of said sleeve, placing a moisture permeable enclosure around said sleeve, said enclosure performing the function of the outer wall of an injection mould and said sleeve performing the function of the inner wall of said mould, with the end portions of said sleeve extending out of said enclosure, injecting colloidal concrete into said mould, compressing the concrete before it has set by creating with fluid means an internal pressure in said sleeve so as to expand said sleeve, releasing said pressure in said sleeve after the hardening of the concrete; placing a flexible annular container on one of said end portions of the sleeve of one of said pipes; fixing said one of said end portions to an end portion of the sleeve of the other of said pipes; placing a second moisture-permeable enclosure around said pipes in the region of said interconnected end portions of the sleeves; injecting concrete into the space defined by said second enclosure and said pipes; injecting under pressure a hardenable material into said flexible container so as to expand said container and compress said concrete in said space, and maintaining said material under pressure until it has hardened. 